I am currently working on designing a Common Source amplifier with NMOS transistors. Unfortunately, I've had a few problems and don't seem to be making any progress. The requirements for the circuit are:
- Driving a load of 500 Ohms
- Maximum drain current of 100mA
- Maximum (W/L) of 1000
- Gain of 20dB (10V/V) at 10kHz
- Input is a 0.1V sine wave at 10kHz with a series resistance of 25kOhms
- Only source available is Vdd@5V (pictured) and GND
Furthermore, my given information is as follows: k = 10^-5 A/V^2, Vt (threshold voltage) = 1V, Lambda = 0.02
Here, I've substituted many different values for R5 and R4, but my general approach is as follows.
- Obtain the Q-Point values of Vgs and Id
- Anaylze the circuit via small signal equivalent - doing so, I arrived at the equation Req = 1/((1/R6)+(1/R5)), where Av = (-𝓰ₘ)(Req), 𝓰ₘ being the transconductance value (which itself is equivalent to sqrt(2*k*Id_q)).
- I calculated the input resistance as R2||R3 to obtain Rg = R2||R3 = 50kOhms.
- For the output resistance, I disconnected the load and assumed the drain resistance to be arbitrarily large so that the output resistance, Ro = R5.
None of my solutions have yielded proper results and I was wondering what I'm doing wrong (any help is appreciated). Thanks.